Feature/emission constraint

[yechenyan]

This new function, process_emission_constraint_inputs(processes_raw), aims to refine the handling of emission constraint data. Below is the detailed workflow and expected transformation:

The input(processes_raw) to the function is a pandas DataFrame as shown below:

process	input	output
battery storage	electricity	electricity
energy transformation unit	ch4	co2, [electricity, heat]
co2, [electricity, heat]	onshore	electricity
x2x_other_dac_ht_1	sec_elec, sec_heat_high	emi_co2_neg_air_dacc
x2x_other_dac_lt_1	sec_elec, sec_heat_low	emi_co2_neg_air_dacc
ind_other_ind_boiler_coal_0	pri_coal	iip_heat_high, emi_co2_f_ind, emi_ch4_f_ind, emi_n2o_f_ind
ind_constraint_co2eq

The return value of the function is a pandas DataFrame, which update the last row as below:

process	input	output
ind_constraint_co2eq	emi_co2_neg_air_dacc, emi_co2_f_ind, emi_ch4_f_ind, emi_n2o_f_ind

Processing Steps:

1. If there's a row in the table where the process is ind_constraintco_2eq, then execute the subsequent steps.

2. Take all the values in the output column that start with emi, remove duplicates, and place them into the input field of the row where the process is ind_constraintco_2eq.

Beside, implement necessary test cases to verify the function's effectiveness and accuracy.

[SabineHaas]

Thanks a lot @yechenyan! looks good to me!
I won't merge, as I am not sure whether it will be part of this adapter or another repo.
However, I have used the function to get all the inputs for the emission constraint, which was very helpful!